This application relates to the vibration damping materials for minimizing vibrations in structural members, and relates in particular to vibration damping laminates.
Structural vibration can occur in a wide variety of structural members. Common deleterious results of such vibration can be mechanical failure of the structural element and/or the generation of acoustic noise. One method commonly employed to reduce such vibration involves the addition of damping material to a vibrating structure. This is referred to as add-on damping, and typically consists of a piece of metal or the like applied to the vibrating structure by means of a pressure-sensitive adhesive. Such add-on damping typically works on the principal of constrained layer damping, which is commonly a three-layer construction consisting of the vibrating source, a viscoelastic layer, such as the pressure-sensitive adhesive, and a constraining layer, such as the piece of metal. The vibrating source provides the unwanted vibrational energy, which causes the outer constraining layer or a piece of metal to shear the viscoelastic layer, causing friction (heat) between the polymer chains of the viscoelastic layer, thereby dissipating the energy. Thus, the viscoelastic layer has two purposes: adhesion of the constraining layer to the vibrating source and vibration reduction.
However, when such an add-on damping material is utilized, pressure is needed during attachment of the damping material to the vibrating source to ensure cold temperature adhesion.
It is known to provide a three-layer damping material, including a constraining layer, a viscoelastic adhesive layer and a magnetic layer, such an arrangement being disclosed, for example, in U.S. Pat. No. 5,300,355 to Mifune et al. In that arrangement, the magnetic layer is formed of a composite which includes, in addition to a magnetic powder, a polymeric material and an adhesive resin. Thus, the composite magnetic layer achieves both a magnetic and an adhesive attachment of the damping laminate to the vibrating source. Furthermore, the material is designed so that the modulus of elasticity of the magnetic layer is equal to or less than that of the adhesive layer so that most of the vibrational damping is effected in the magnetic layer.
Japanese patent publication no. 3-47750, referred in U.S. Pat. No. 5,300,355, discloses a similar arrangement, wherein the metal layer is primed and coated with a rust preventive coating.